How to ‘see’ quantum entanglement

WE MAY soon be able to watch the spooky workings of quantum mechanics with our own eyes.

Nicolas Brunner of the University of Geneva, Switzerland, and his colleagues wanted to find out whether human eyes could see the signs of entanglement – a quantum property that allows two particles to become inextricably linked so that making a measurement on one instantaneously affects its partner, no matter how far apart they are.

The effect can demonstrated in a simple experiment. A pair of entangled photons, A and B, are generated and then sent along different paths. Each photon meets a beam splitter, which could send the photon either left or right. The two photons always seem to choose the same direction, because the photon that reaches a splitter first, and is therefore “measured” first, somehow triggers a change in its entangled counterpart.

Although individual photons are not visible to the human eye, the team calculated that if they used 100 entangled pairs of photons, their collective light would be bright enough to see. A human observer would be unable to distinguish individual entangled pairs, says Brunner, yet after the experiment has been completed it should be possible to analyse all the reported sightings and calculate the probability that various pairs matched up (www.arxiv.org/abs/0802.0472).

The team hopes to carry out an experiment with people soon. “With the human eye, you really can access the quantum world,” says Brunner.

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